Tonycom Hi there!
As a first step (if you haven't already), I'd highly recommend reading this section of the FAQ on the GrapheneOS website:
Some (a lot, really) of apps only do notifications via FCM, which requires Google Play Services. If you need notifications for these apps, you'll need to install Sandboxed Google Play. It's a very well implemented option that allows you to use these services in a secure and relatively private manner.
However, other apps do provide another option in addition to FCM, such as SIgnal. If you install Signal without having play services on the device, Signal will default to its own notifications implementation. Do note that this implementation is more battery hungry, so if you're going to be using Sandboxed Google Play for other apps anyway, you should install Signal after installing Sandboxed Google Play, so that it can take advantage of it.
I hope that helps!